A basic optical speed sensor, also known as an optical encoder or tachometer, is a device used to measure the speed or rotational motion of a mechanical component. It utilizes the principles of light sensing and interruption to determine the speed at which an object is moving. Here's how it typically operates:
Light Source: The sensor consists of a light source, usually an infrared LED (Light Emitting Diode). This LED emits a focused beam of light towards a target surface or a rotating object.
Rotating Disc or Object: The object whose speed you want to measure has a disc or pattern attached to it. This disc is often referred to as a "code disc." This disc contains alternating transparent and opaque segments (slots) arranged in a circular pattern around its circumference.
Photodetector: Positioned on the other side of the disc is a photodetector, which is typically a phototransistor or a photodiode. The photodetector's purpose is to detect changes in light intensity caused by the alternating transparent and opaque segments of the rotating disc.
Interrupted Light Beam: As the disc rotates, its alternating transparent and opaque segments pass between the light source (LED) and the photodetector. When a transparent segment is aligned with the light beam, the light passes through and reaches the photodetector, generating an electrical signal. When an opaque segment passes through, the light is blocked, and the photodetector receives little to no light, resulting in a different electrical signal.
Signal Generation: The interruptions in the light beam caused by the rotating disc generate a square wave electrical signal from the photodetector. Each complete cycle of the square wave corresponds to one rotation of the disc. The frequency of this square wave is proportional to the rotational speed of the object.
Signal Processing: The generated square wave signal is then processed by electronic circuitry to measure its frequency. The frequency of the signal directly correlates with the rotational speed of the object. By knowing the number of slots on the code disc and the timing of the signal transitions, the speed of the rotating object can be accurately calculated.
Speed Calculation: The speed of the object can be determined by converting the frequency of the square wave signal into rotations per minute (RPM) or any other appropriate unit of speed. The conversion factor depends on the number of slots on the code disc and the specific design of the sensor.
Output: The calculated speed information can be displayed on a digital screen, transmitted to a control system for further processing, or used in various applications where speed measurement is essential.
In summary, a basic optical speed sensor operates by emitting a light beam towards a rotating disc with alternating transparent and opaque segments. The interruptions in the light beam are detected by a photodetector, generating an electrical signal that is converted into speed information through signal processing and calculation.